It is known from German Published Application 3,441,934 (U.S. Pat. No. 4,619,966) to prepare solutions or dispersions of polyisocyanate addition products in which anionic structural units of the formula ##STR1## which ensure the solubility or dispersibility in water are incorporated. These solutions or dispersions are prepared by reacting an organic polyisocyanate with ammonium salts of cyanamide. The ammonium salts may be added as such or prepared in situ by using cyanamide with suitable bases. When sheet products produced from these solutions or dispersions are cross-linked by heat, they give rise to water resistant and solvent resistant reaction products or coatings after elimination of the base.
In practice, it has been found that this prior art procedure has certain disadvantages for the production of sheet products or coatings. Those disadvantages include:
the solutions or dispersions tend to foam up; PA1 so called "boiling blisters" are liable to form during the stoving process, depending on the atmospheric conditions; PA1 the production of perfect cross-linked and therefore solvent resistant and water resistant films requires high stoving temperatures of about 180.degree. C.